The invention relates to a device for controlling the spacing of the plates on a bridging arrangement for expansion joints in bridges or the like, which arrangement has one or more plates running parallel between the edge beams that define the expansion joint and mounted on cross-members bridging the expansion joint.
There are, in practice, numerous types of control devices for bridging arrangements of the type mentioned. Owing to their noiseless functioning, those control devices having elastomeric control elements which flexibly support adjacent plates with respect to one another and the outer plates with respect to the edge beams have become widely used.
In one previously proposed control device of the type mentioned at the beginning (see DE-OS No. 30 17 048), there are used as control elements shear-deformable elastomeric blocks which at the same time form load-transmitting bearing parts between the plates and the cross-members arranged underneath them. In such constructions, the control device is therefore part of the load-supporting system, and all the components of the bridging arrangement must therefore be a plurality of connectors that are resistant to bending; a plurality of resilient members, each secured at one end to a said edge beam or to a said plate and at the other end to a said connector; each connector connecting said resilient members secured to one said edge beam and to a said plate or to two said plates to one another in such a manner that said plate is coupled to said two edge beams or each said plate is coupled to a said edge beam and to an adjacent said plate or to two adjacent said plates, by means of a said connector through said resilient members, said resilient members deforming resiliently in shear in response to changes in the separation between said plates and said edge beams; and said resilient members and said connectors forming at least one control chain connecting all said plates to one another and to said two edge beams.
Such a control device may comprise substantially only two different components, namely the resilient members and the connectors that are resistant to bending. The former are preferably each formed as a block of elastomer which is connected either directly or via anchoring parts to a plate or an edge beam and/or to the connector. The connectors are components that are subject to stress in tension and bending and are designed to ensure the necessary parallel guiding of the resilient members.
Mounting the control device is therefore very simple; owing to the fact that it can be secured to the underside of the plates or edge beams, there are no spatial problems with regard either to accommodating the components of the control device or to mounting them.
The connectors that are resistant to bending preferably consist of metal or a rigid plastics material. A suitable material for the resilient members is rubber or polyurethane.
Depending on the design of the bridging arrangement, two constructions of the control chains having different extreme rest positions are especially suitable.
In one construction the shear stress in each resilient member of a control chain is zero or virtually zero when the joint is closed and increases as the degree of opening of the joint increases.
In the second arrangement the shear stress in each resilient member of a control chain is zero or virtually zero when the joint is open to its maximum extent and increases as the joint closes.
In principle, however, it is also possible so to design the resilient members that their shear stress is zero or virtually zero in an intermediate position of the joint.
It is generally advantageous to provide at least two control chains at a distance from each other. Owing to the alternately acting shear forces, the plates are then held in position without torsion with respect to a vertical axis, that is to say parallel to one another and to the two edge beams fixed in the edges of the joint. To simplify the construction of the bridging arrangement, the edge beams can have the same design as the plates.
Preferably, an even number of control chains is provided, chains having maximum stress when the joint is closed and chains having maximum stress when the joint is open being arranged alternately. As a result of this alternating arrangement of the two different types of control chains, the construction of which is explained above, the control chains exert a constant bias on the plates in all positions of the joint since a decrease in the controlling forces exerted by one control chain is compensated for by an increase in the controlling forces exerted by the other control chain as the degree of opening of the joint varies.
The invention also provides a bridging arrangement for an expansion joint in a bridge or the like, comprising edge beams that define said expansion joint, cross-members bridging said expansion joint, one or more plates running parallel between said edge beams and mounted on said cross-members, and a control device according to the invention forming at least one control chain connecting all said plates to one another and to said two edge beams.
The invention further provides an assembly comprising two edge beams extending generally parallel to one another and spaced apart in a direction perpendicular to their length; at least one plate generally parallel to and between said edge beams; a plurality of resilient members, secured singly to each said edge beam and in pairs to each said plate; a plurality of connectors resistant to bending, each connecting a respective said resilient member of a said plate to a respective resilient member of an adjacent said plate or of a said edge beam; said resilient members and said connectors forming at least one control chain so connecting all said plates and said edge beams as to tend to maintain said plates at equal spacings from one another and from said edge beams, said resilient members being stressed primarily in shear, and said assembly being suitable for use as a bridging arrangement for an expansion joint in a bridge or the like.
Any of the optional and advantageous features disclosed for a control chain according to the invention may of course be applied, mutatis mutandis, to a bridging arrangement or an assembly according to the invention.